Whitmore Lake is a census-designated place (CDP) and unincorporated community in the U.S. state of Michigan. The community spans the boundary between Green Oak Township in Livingston County and Northfield Township in Washtenaw County. The population of the CDP was 6,423 at the 2010 census. The Whitmore Lake post office, with ZIP code 48189, serves a larger area than that defined by the CDP and includes portions of southeast Hamburg Township, northeastern Webster Township, and larger parts of Green Oak and Northfield Townships than are included in the CDP.